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synthtel2
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Chimney-effect low-noise cases

Thu May 18, 2017 9:40 pm

I thought about entering this in the napkin sketch contest, but I don't have any need for a new case and it seemed a bit more serious than the usual fare there. Not serious enough that I'll likely bother building it, but serious enough that it deserves its own thread, I think.

The basic idea is to get a floor-standing tower, maybe 7.5" ID and 4+ feet tall, leave the top and bottom open to airflow, and build a computer in the bottom of it. The more heat the components produce, the more air passively flows up the tower. In a simple form, it should be able to replace case fans pretty well. In a more advanced design, it could be ducted so that all the air has to flow through the CPU/GPU heatsinks, potentially resulting in a mostly passive yet very powerful system.

When thinking of more specific layouts, I can't quite seem to hit all the design points I want. They are (in no particular order): CPU and GPU as low as possible for maximum space efficiency, PSU and SSDs below CPU and GPU for better reliability, filtered air intake, ability to fit full-length graphics cards, easy access to ports, compact but stable (probably round) footprint, and support for ducted cooling of individual components. I've got designs that can hit just about any five of those seven points at once. My favorite so far hits everything except the easy port access:

Image

That's with a PCI-e extender to wrap the graphics card around behind the mobo, like in the A4-SFX. I think that's about as good as cooling is going to get in that form factor, especially since the graphics card can be isolated from everything else. The trouble is that all the ports are upward-facing, so the chimney will have to be detachable somehow and have a hole in its side for cables. That hole will have to have some kind of grommet to block most airflow. It also has some requirements for the CPU and GPU coolers, though I don't think they're particularly onerous ones. (A blower GPU cooler would probably work better, but doesn't seem essential.) If it's all working properly and using conventional fan controls, it'll probably have normal amounts of fan noise when load first shows up, but when under a sustained load like gaming it should drop to very low noise as passive airflow through the heatsinks picks up (assuming fan controls are set up suitably). Quicker response should be achievable by narrowing the inside of the tower just above the cable routing area, and not expanding it to full width again until a ways up.

Thoughts?
 
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Re: Chimney-effect low-noise cases

Thu May 18, 2017 9:53 pm

If I get a new case I am likely going to be making my own next time. I want one where the mobo lays down flat and the case is cooled by a single 40 or 50cm fan. With a nice big CPU/GPU heatsink you could cool them both with that single fan probably. I'd probably test angling a board of some kind down so that the air gets all pushed into the heatsinks. I don't know if it would help or not, but at that point it would be very easy to test.

As to your case, it's an interesting idea. I wonder how well it would work.
 
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Re: Chimney-effect low-noise cases

Thu May 18, 2017 10:14 pm

Apple did theirs in a custom case for more reasons than just the bizarre aesthetics: you need a lot of heatsink surface area to get a good flow established. Getting heat to rise from a hot surface is trivial, but getting enough to make a meaningful difference requires long, vertical fins. My suggestion would be watercooling with transfer coils mounted to a large aluminum extrusion that looks like this or this instead of a fan-cooled radiator.
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synthtel2
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Re: Chimney-effect low-noise cases

Thu May 18, 2017 10:27 pm

Giant fans are also good, yeah.

You need a lot of heatsink thermal mass to avoid the fan use on warm-up, but steady-state airflow isn't tied to heatsink area much at all. A particular exhaust temperature will create a particular amount of static pressure, according to how much less the warmed air in the tower weighs than the ambient air outside. The big advantage of extra heatsink area is that less airflow is required, so exhaust temperature (and component temperatures) can be lower. The Mac Pro doesn't have much tower and is still very dependent on its fan, but it would be pretty cool to add a tower to the top of one.

To look at it another way, when you mount a heatsink like that vertically in free air, you get a bit of this same effect, but only across the height of the heatsink in question. I'm trying to get that effect across three or four feet.
Last edited by synthtel2 on Thu May 18, 2017 10:32 pm, edited 1 time in total.
 
slowriot
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Re: Chimney-effect low-noise cases

Thu May 18, 2017 10:32 pm

Silverstone has used a similar approach with the FT03 and FT03-Mini cases. They're interesting but flawed, definitely some room for improvement.
 
synthtel2
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Re: Chimney-effect low-noise cases

Thu May 18, 2017 10:38 pm

Nice, I hadn't seen those before. An FT03-mini with a three-foot vertical extension and some extra ductwork sounds about right.
 
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Re: Chimney-effect low-noise cases

Thu May 18, 2017 11:10 pm

Having a PC's top portion open when it's standing on the floor (presumably close to you) will let too much noise through, thereby making the whole "silence" thing moot.

If the computer is on a desk it's less of an issue, but then you have the problem where the top portion needs to not be complete "open" to, again, not let much noise through.
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synthtel2
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Re: Chimney-effect low-noise cases

Thu May 18, 2017 11:59 pm

What's making noise? :wink:

PSU, CPU, and GPU fans will still exist, but if this works as planned, they'll barely need to do anything. I'd much rather have some fans idling at 500-750 RPM in open air near me than try to muffle fans that need to run 1500 RPM.

In addition, the exhaust of this is supposed to be closer to the ceiling than the floor, and it's a 7.5" diameter port. Any sounds past 1.5 kHz or so should be coming out of that with a lot of directionality, giving the ceiling a good chance to absorb and re-scatter them before they get anywhere important. There's also a thing equivalent to the backplate of a normal case in between the fans and that port.

If you're running serious OCs or just have very high standards for silence, there's plenty of space to put a proper muffler in the tower. In fact, let's say the design now by default includes the narrowing of the lower interior tower wall for better responsiveness, the difference is made up by a hollow wall with some kind of acoustically absorbing fill, and the inner wall is perforated. Problem extra-solved. :)
 
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Re: Chimney-effect low-noise cases

Fri May 19, 2017 8:35 am

Wait, I could swear the Napkin Sketch Contest was over. Heck, I was part of the jury :P
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Re: Chimney-effect low-noise cases

Fri May 19, 2017 9:09 am

Hmmm is it really needed?

I have an old Lian-Li PC-7FNW, front case fan is an arctic cooling 140mm 800rpm max, and my one exhaust fan is a scythe 900rpm, which the same fan is also on my noctua cpu cooler.

On the BIOS fan control they usually run around 400rpm and are inaudible. I don't even have a HDD in it because I'm so anal about noise, well especially HDD noise ;)
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Re: Chimney-effect low-noise cases

Fri May 19, 2017 9:31 am

When ambient is hot, the fan in my window makes far more noise than the box (P182) will ever make, and when ambient is cool (I heat to 65F in winter), it's still mostly silent.
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morphine
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Re: Chimney-effect low-noise cases

Fri May 19, 2017 10:24 am

Hardly a fair comparison, Ned. The P182 is a big, lumbering beast with sound-proofed side panels that weigh as much as entire cases. I still love mine, but it's since been relegated to NAS duties atop an IKEA shelf stand.
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Re: Chimney-effect low-noise cases

Fri May 19, 2017 10:27 am

Who said I was playing fair? :wink:
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Re: Chimney-effect low-noise cases

Fri May 19, 2017 10:28 am

4' tall seems way beyond practical even for effective passive cooling. Something like a Noctua D15 will be inaudible in most all environments. But if you absolutely need no fans then it would almost be more space efficient to just go with a mineral oil tank.
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